Evaporating and depolymerizing device



April 18, 1967 P, sARRAT ETAL EVAPORATING AND DEPOLYMERIZING DEVICE Filed June 50, 1964 IW//I/ I f// l0 INVENTORS PIERRE SAR/Qm- BY Rom/v0 Vu/LEMEY @mZ/9W ATTORNEYS United States Patent O 4 Claims. (ci. 122-33) The present invention relates to a device for evaporation and depolymerization or simple evaporation which permits the possibility of obtaining in continuous operation a constant delivery of vapor which is super-heated at constant temperature and under conditions of pressure which cannot be obtained by means of a liquidvapor equilibrium. This `device is applicable in particular to all those liquids whose vapor pressures increase very rapidly with the temperature (ACN, HF, etc.).

The said evaporating and depolymerizing device is essentially characterized in that it comprises a doublewalled evaporating vessel, a system of depolymerization of vapors consisting of a metallic coil which communicates with the evaporating vessel, a system for the forced circulation of `an auxiliary liquid between the double wall of the evaporating vessel and around the coil for the precise regulation of temperature and a sonic venturi tube for the discharge of depolymerized vapors.

In accordance with another characteristic feature, the depolymerization system is tted with a heating pin of the electric resistance type regulated by a measuring thermometer probe which sets the temperature at a predetermined level. In addition, the circulation system for the auxiliary liquid which advantageously consists -of paraffin oil is coupled to a surge tank titted with a the-rmocouple which serves to determine and to record at any moment the temperature which is reached within the apparatus.

The injection in liquid phase of the product to be evaporated is carried out by means of a storage vessel which is maintained at constant pressure and at a temperature which is lower than the boiling point. Constant delivery is achieved by utilization of a sonic venturi tube which is located at the outlet of the evaporating and depolymerizing unit and which consists of a combining and diverging nozzle, the throat of which is calibrated as a function of the requisite range of flow rates. It should be noted that this device is based on the pressure equilibrium between the liquid and the vapor within the storage vessel and that of the gaseous phase throughout the apparatus as a whole.

Further characteristic features which will serve to bring out the advantages of the device according to the invention, especially in its application to the evaporation and depolymerization of hydrouoric acid, will become more readily apparent from a study of the following description of one example of embodiment which is given by way of indication and not in any limiting sense.

In the accompanying drawings, the single figure represents a diagrammatic View in vertical cross-section of an evaporating and depolymerizing device as constructed in accordance with the invention.

As can be seen from this gure, the apparatus is composed of an evaporating vessel 1 consisting of a cylindrical metal tank of copper, for example, in the interior of which liquid is admitted through a pipe 2, such as, hydrofluoric acid in liquid -phase which is injected from a storage vessel 20 maintained at a temperature below 19 C. and at constant pressure. The vessel 1 is surrounded by a coaxial casing 3 which forms an annular space between the internal surface thereof and the vessel 1. The vessel 1 and its outer casing 3 are sealed at the top by means of a closure plate 4 traversed -by a conduit 5 which connects Patented Apr. 18, 1967 ICC the interior of the vessel 1 to a coil 6 housed within acylindrical box 7.

The internal volume of the said box 7 communicates through pipes 8 and 9 with the -annular space which is formed between the vessel 1 and its outer casing 3 so as to form a circulation loop for a liquid having suitable density, for example paraffin oil, which is intended to permit of accurate regulation of temperature around the vessel 1 and the coil 6. An immersed-rotor pump 10 effects the circulation of oil through all the pipes whilst a helix 11 which is secured to the outer wall of the vessel 1 permits the circulating oil to be continuously renewed within the annular space which is provided around said vessel.

The top portion of the box 7 is connected by means of a conduit 12 to a surge tank 13 which prevents any detrimental overpressure within the oil circulation system; a thermocouple probe 14 which is immersed in the oil permits the continuous measurement of the oil temperature.

A heating pin 15 is disposed axially of the coil 6 in which there takes place the depolymerization proper of the acid vapors derived from the vessel 1, as will be explained hereinafter. The said heating pin is regulated by an expansion-type thermometer probe 16 in such manner as to obtain a given temperature to within i2". (The operating temperature is Ipreferably fixed at C. in the case of hydrofluoric acid.) At the outlet of the coil is mounted a pressure gauge 17 and a thermometer probe (which has not been shown in the drawing) which provides a means of checking the constancy of both pressure and temperature and consequently of knowing the vapor ow rate during operation.

Finally, the apparatus as a whole is surrounded by a suitable layer 18 of an appropriate heat-insulating material.

The operation of the device is `as follows: hydrofluoric acid is admitted in liquid phase through the -pipe 2 within the interior of the vessel 1 at a predetermined pressure which is a function of the pressure prevailing within a thermostable storage tank 20 which supplies the acid, said tank being tted with a conduit 21 through which a gas such as nitrogen, for example, is admitted and is also fitted with a pressure gauge 22. As a result of the temperature rise which is due to the circulation of oil around the vessel 1, the vapor pressure of the acid increases until it balances the pressure of the liquid phase, thereby producing a remarkably stable automatic regulation. The -acid vapors escape through the pipe 5 and pass into the coil 6 in which they are depolymerized. By means of a sonic venturi tube 19 which is mounted on the end of the coil 6, there is produced at the outlet of the apparatus a rangey of gas flow rates which is prefectly stable as a function of the caliber of said sonic venturi tube and las a function of the pressure within the storage vessel. By way of example, in the case of an operating temperature of 120 C. within the depolymerizer and a pressure within the storage vessel which is comprised between 0 and 5 kgs/cm?, there can be obtained at the outlet of the `apparatus a constant gas flow with automatic pressure compensation which is comprised between 0 and 1.5 kgs/hour.

It will 4he readily understood that the invention is not limited to the form of embodiment which has been described and illustrated solely by way of example and which an be employed for the purpose of vaporizing other compounds such as the following: B4H10, BCl3, HCN, FEBI, CS2, FGMO.

What we claim is:

1. Apparatus for evaporating and depolymerizing liquids whose vapor pressure increases very rapidly with temperature comprising in combination (a) an annular vessel including means for storing said 3. An apparatus according to claim 1 wherein the liquid at constant pressure and for maintaining said evaporating Vessel, dcpolymerization means and heat exliquid at a temperature slightly below its boiling change liquid circulation system are surrounded by a point; thick layer of heat insulating material.

(b) a second annular vessel for evaporating said liquid; 4. An apparatus according to claim 1 in which the (c) means for transferring a portion of said liquid to 5 heat exchange liquid circulation system includes a surge said second vessel; tank to prevent overprcssure and controlled heating means (d) means for communicating with said evaporating for maintaining the temperature of the liquid at a constant vessel for depolymerizing said evaporated vapors contemperature. sisting of a metallic coil and a housing for said coil;

(c) means for the controlled heating and forced cir- 10 References Cited by the Examiner culation of heat transfer fluid through the annular UNITED STATES PATENTS space of the evaporating vessel and through the ho'usng around said depolymerizing coil for maintaining 2,162,746 6/1939 Randel 122 33 a precise temperature in both said second vessel and 2,703,072 3/1955 Throckmorton et al. 122 33 Coil and 15 3,055,347 9/1962 Bailey et al. 122-33 tf) a sonic venturi communicating with the exit of said 3,193,917 9/1963 Bauelet HL 12:2 33 X depolymerizing coil for the discharge of depolym- 3 1111935 11/1963 Loebel 122 23 erized vapors.

2. An apparatus according to claim 1 wherein the heat KENNETH W, SPRAGUE, Primary Examine); exchange uid is parain Oil. 20 

1. APPARATUS FOR EVAPORATING AND DEPOLYMERIZING LIQUIDS WHOSE VAPOR PRESSURE INCREASES VERY RAPIDLY WITH TEMPERATURE COMPRISING IN COMBINATION (A) AN ANNULAR VESSEL INCLUDING MEANS FOR STORING SAID LIQUID AT CONSTANT PRESSURE AND FOR MAINTAINING SAID LIQUID AT A TEMPERATURE SLIGHTLY BELOW ITS BOILING POINT; (B) A SECOND ANNULAR VESSEL FOR EVAPORATING SAID LIQUID; (C) MEANS FOR TRANSFERRING A PORTION OF SAID LIQUID TO SAID SECOND VESSEL; (D) MEANS FOR COMMUNICATING WITH SAID EVAPORATING VESSEL FOR DEPOLYMERIZING SAID EVAPORATED VAPORS CONSISTING OF A METALLIC COIL AND A HOUSING FOR SAID COIL; (E) MEANS FOR THE CONTROLLED HEATING AND FORCED CIRCULATION OF HEAT TRANSFER FLUID THROUGH THE ANNULAR SPACE OF THE EVAPORATING VESSEL AND THROUGH THE HOUSING AROUND SAID DEPOLYMERIZING COIL FOR MAINTAINING A PRECISE TEMPERATURE IN BOTH SAID SECOND VESSEL AND COIL AND (F) A SONIC VENTURI COMMUNICATING WITH THE EXIT OF SAID DEPOLYMERIZING COIL FOR THE DISCHARGE OF DEPOLYMERIZED VAPORS. 